After the accomplishment of the human genome projects, ardent researches have been carried out on proteome. The term “proteome” encompass any proteins which are produced via translation in certain cells, organs, etc. One example of the researches on proteome is profiling of a protein.
One of most common techniques for profiling a protein is 2-dimension electrophoresis of the protein. Proteins have different electric charges and molecular weights unique to themselves. From proteome, which is a mixture of many kinds of proteins, the proteins may be separated based on the electric charges or molecular weights. However, it is possible to perform protein separation from the proteome with higher resolution for more kinds of the proteins by separating the proteins from the proteome based on electric charges and molecular weights in combination.
The 2-dimensional electrophoresis include two electrophoresis steps: isoelectric focusing electrophoresis for separating proteins based on their electric charge differences; and slab gel electrophoresis (especially, SDS-PAGE) for separating the proteins based on their molecular weight differences. Moreover, the 2-dimensional electrophoresis may be carried out with a sample prepared with or without a denaturing agent. As such, the 2-dimensional electrophoresis is an excellent technique capable of separating several hundreds kinds of proteins in one time.
In the 2-dimensional electrophoresis, a sample is subjected to the isoelectric focusing electrophoresis in a first dimension gel. Then, the first dimension gel is transferred to be applied to a second dimension gel in which the sample is subjected to the molecular-weight-based separation. Generally, the first dimension gel for the isoelectric focusing electrophoresis is very thin in comparison with its width and length. Therefore, it is difficult to recognize which side is the front side or back side of the gel, and in which way the gel has a pH gradient. Further, the gel is easy to be warped or twisted and thus is poor in shape stability. This would be a cause of poor reproducibility of results of the electrophoresis. Further, handling of the first dimension gel is not easy, which poses an impediment to an effort of improving the transfer of the first dimension gel to the second dimension gel in terms of positioning accuracy. Moreover, in case where the second dimension separation is carried out with SDS-PAGE, it is required to perform equilibrating (SDS treatment and reduction) treatment (chemical treatment) to the first dimension gel after the first dimensional electrophoresis, so that the proteins in the first dimension gel will be able to migrate through the second dimension gel. Due to the need of such treatment to the first dimension gel, the 2-dimensional electrophoresis produces different results depending on operator's proficiency.
As described above, the 2-dimensional electrophoresis is an excellent technique, yet it requires the operator thereof to be highly skilled in operating it. The dependency of the operator's proficiency makes it difficult for the 2-dimensional electrophoresis to obtain quantitative data with good reproducibility.
In order to overcome this problem, techniques to automate the 2-dimensional electrophoresis have been developed (see Patent Literature 1 and Non-Patent Literature 1).